Objective: The purpose of this study was to assess the level of psychological stress and the perceived stressors among the undergraduate clinical dental students of Shiraz School of Dentistry. Materials and Methods: This study was conducted during the second semester of the academic year 2018– 2019 at Shiraz School of Dentistry, Shiraz University of Medical Sciences, Iran. The study group consisted of 150 dental clinical students. The participants were surveyed via the validated Depression, Anxiety, and Stress Scale (DASS-21) and the Dental Environment Stress (DES) questionnaires. One-way ANOVA, post hoc Tukey’s test, repeated measure ANOVA, Holm‐Sidak’s test, and t-test were performed to analyze the data after the normality of the data was checked by Kolmogorov–Smirnov test. The P values of less than 0.05 were considered as statistically significant. Results: No significant differences were observed among the dental students with different academic levels in terms of depression and anxiety scores (P=0.057 and 0.154, respectively). The lowest and highest stress scores were observed among the sixth- and fifth-year students, respectively (P values < 0.05). The scores of the stressors associated with the academic factors were significantly higher than those of the other domains (P< 0.05) except for that of the clinical education domain (P=0.070). The females showed significantly higher DES scores (P values < 0.05). Conclusion: The highest and lowest stress levels were observed among the fifth- and sixth-year students, respectively. The primary sources of stress were academic factors and clinical education. The females expressed higher levels of stress in certain areas of dental training.

Aim: This study was conducted to evaluate the effect of three nanoparticle solutions used as final root canal irrigants on the fracture resistance of endodontically treated roots. Materials and Methods: Sixty intact single-rooted premolar teeth were used after removing the crowns below the cementum–enamel junction to standardize the length of the remaining roots to 13 mm. After instrumenting the roots using ProTaper Universal rotary instruments up to size F4, the roots were randomly divided into six groups (n=10) according to the final irrigating solutions: Group 1: normal saline; Group 2: 2% chlorhexidine (CHX); Group 3: 17% EDTA+2.5% NaOCl; Group 4: 17% EDTA+0.1% silver nanoparticle (SNP) solution; Group 5: 17% EDTA+0.1% titanium dioxide nanoparticle (TNP) solution; Group 6: 17% EDTA+0.1% zinc oxide nanoparticle (ZNP) solution. After filling the root canals with gutta-percha and AH Plus sealer, the fracture resistance (FR) values were measured. The data were subjected to the one-way analysis of variance and the Tamhane post hoc test (p=0.05). Results: EDTA + NaOCl had the lowest FR value, followed by normal saline and CHX (p values < 0.05). No significant difference was found between the FR of roots irrigated with CHX and normal saline (p > 0.05). The application of nanoparticles (SNP, TNP, and ZNP) was associated with a significantly greater FR than that of other irrigation solutions (p values < 0.05). Conclusion: The final irrigation of root canals with nanoparticles enhanced the fracture resistance of the endodontically treated roots. The lowest FR value was observed for NaOCl.

The aim of this study was to investigate the mechanical properties and dentin microshear bond strength of a conventional glass ionomer cement (GIC) compared to GIC supplemented with silver nanoparticles (SNPs) at 0.1% and 0.2% (w/w). SNPs were incorporated into a conventional GIC at 0.1% and 0.2% (w/w). The unmodified GIC was used as the control group. Compressive strength, flexural strength, and micro-shear bond strength (µSBS) to dentin were evaluated using a universal testing machine. Surface microhardness was determined using a Vickers microhardness tester. The data were analyzed using one-way analysis of variance (ANOVA) and Tukey's test. GICs containing 0.1% and 0.2% (w/w) SNPs significantly improved compressive strength, surface microhardness, and dentin µSBS compared to the unmodified GIC (p<0.05). A significant increase in the flexural strength was found for the GIC containing 0.2% (w/w) SNPs (p<0.05). However, the GIC containing 0.1% (w/w) SNPs did not affect flexural strength. GIC supplemented with SNP is a promising material for restoration because of its improved mechanical and bond strength properties. Therefore, it may be suggested for use especially in higher stress-bearing site restorations. Key words:Glass ionomer cement, mechanical properties, micro-shear bond strength, silver nanoparticle.

Objectives Inner carious dentin is specified with decreased minerals and collagen cross-links but without protein denaturation. Current minimally invasive dentistry concepts recommend removal of only the outer layer of carious dentin and biomodification of repairable inner carious dentin. The present study aims to investigate the possibility of functional repair of this layer using silver diamine fluoride (SDF) and grape seed extract (GSE). Materials and Methods Molar teeth with occlusal caries were used to prepare caries-affected dentin specimens for hardness and elastic modulus measurements. The specimens of each test were divided randomly into four equal groups. In the GSE group, the specimens were immersed in 6.5% GSE solution for 10 minutes. In the SDF group, the specimens underwent a topical application of a 30% SDF. In the GSE+SDF group, first the specimens were immersed in GSE and then exposed to SDF. In the SDF+GSE group, first SDF was applied and then the specimens were immersed in GSE. Microhardness measurements were taken at baseline and after treatment. A control group with distilled water treatment was also prepared for elastic modulus measurements. Statistical Analysis One-way analysis of variance and post-hoc tests were used for statistical analysis. Results There were significant differences in H₁-H₀ (final hardness—baseline hardness) among the groups. Baseline and final hardness of each group was also significantly different (SDF>SDF+GSE>GSE>GSE+SDF). Elastic modulus of SDF and SDF+GSE increased compared to the control group. Conclusions SDF and SDF+GSE treatment can be recommended to increase hardness and elastic modulus of caries-affected dentin.

Aim: This study was conducted to evaluate the effects of three nanoparticle solutions used as dentin pretreatments on the microshear bond strength (μSBS) of a conventional glass ionomer cement (GIC) to dentin. Materials and Methods: Ninety intact human molars were used after sectioning their occlusal surfaces to expose flat dentin surfaces. The specimens were randomly assigned to nine groups (n = 10). Group A was the control group (without using the cavity disinfectant). In groups B, C, D, and E, the prepared dentin surfaces were treated with 1 cc 2% chlorhexidine (CHX), 0.1% silver nanoparticle (SNP), 0.1% titanium dioxide nanoparticle (TNP), and 0.1% zinc oxide nanoparticle (ZNP) solutions for 1 minute, respectively, before applying the conditioner. CHX, SNPs, TNPs, and ZNPs were applied for 1 minute after applying the conditioner in groups F, G, H, and I, respectively. The specimens were restored with a conventional GIC and underwent μSBS testing after 24 hours. The data were analyzed using the one-way analysis of variance and Tukey’s test (p=0.05). Results: The applications of the nanoparticles (SNP, TNP, and ZNP) after the conditioner were associated with significantly greater μSBS values compared to that of the control group (p values < 0.05). Significantly higher μSBS values were observed when TNP or ZNP was applied after the conditioner compared to their applications before the conditioner (p values < 0.05). The highest μSBS values were observed when TNP was applied after the conditioner. Conclusion: Dentin pretreatment with the nanoparticles after applying the conditioner enhanced the bond strength of the GIC to dentin compared with the control group. The best results were obtained for the TNPs applied after the conditioner.

Objectives: This study aimed to synthesize and characterize mesoporous zinc oxide nanoparticles (ZnO NPs) and also to evaluate the cytotoxicity of mesoporous ZnO NPs on L929 mouse fibroblast cell lines using 3‐(4,5‐ dimethylthiazol‐2‐yl)‐2,5‐diphenyl tetrazolium bromide (MTT) assay.Materials and Methods: The synthesized mesoporous ZnO NPs were extensively characterized using X‐ray diffraction analysis (XRD), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) analysis, field emission scanning electron microscopy (FESEM), energy dispersive X‐ray spectra (EDAX), Fourier‐transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). The cytotoxicity of mesoporous ZnO NPs was assessed by MTT assay. The study groups for cytotoxicity assay were normal saline, 0.1% calcined mesoporous ZnO NP solution, 1% calcined mesoporous ZnO NP solution, 0.1% noncalcined mesoporous ZnO NP solution, 1% noncalcined mesoporous ZnO NP solution, 0.1% ZnO NP solution, 1% ZnO NP solution, 2% chlorhexidine, and phosphate‐buffered saline (PBS). The percentages of mean ± standard deviation of viable cells were analyzed.Results: Characterization of mesoporous ZnO NPs revealed that all the particles were in a more or less spherical shape with a wide particle size distribution of 70–100 nm. TEM image showed the uniformed and aggregated ZnO NPs with a typical size of 10–15 nm. BET analysis showed a mesoporous structure for the prepared mesoporous ZnO NPs. According to the MTT assay, chlorhexidine had the lowest cell viability percentage. Cell viability percentages of 0.1% mesoporous ZnO NP solutions (calcined and noncalcined) were statistically, significantly higher than 0.1% ZnO NP solution (p < .05). Cell viability percentages of 0.1% calcined and noncalcined mesoporous ZnO NP solutions and 0.1% ZnO NP solution were statistically, significantly higher than the 1% solutions (p < .05).Conclusion: Mesoporous ZnO NPs exhibited less cytotoxicity against L929 mouse fibroblast cell lines compared to CHX and ZnO NPs, hence are safe to use.